Research On Constant Output Power Based On Double Pick-ups In Dynamic Wireless Power Transfer System

Dynamic wireless power transfer(DWPT),be able to realize the contactless dynamic transmission,through the magnetic coupling between transmitter coils on the ground and pickup coils on the moving vehicle.In the high-speed railway transportation,it is expected to replace the pantograph or third rail as a novel power-supply mode.For electric vehicle(EV)and trams,the continuous charging will be able to reduce the requirements for storage battery and improve the mileage of vehicle.At present,DWPT has been applied in EV,railway transportation,et al,and has gradually been the focus of whole energy and transportation.Firstly,the research status of DWPT system at home and broad is introduced in this paper,including the design and optimization of both compensation network,coupler and control strategy.Both each circuit part and system frequency have been explained,and the voltage or resistance conversion relations of the important transfer parts have also been derived.Differ from the static system,both the coupler parameters and reflect impedance vary greatly in the DWPT system,which lead to some of unstable characterstics such as the load voltage,current,power and efficiency.In order to stabilize the output power in the forward moving,a constant output power DWPT system based on double pick-ups has been designed in this paper,which can be applied better to railway transportation.Primary and secondary side are both considered,compensation network,coupler structure and secondary side control strategy are combined effectively.Firstly,the magnetic field should be stable and independent of reflect impedance,so the LCC structure with the characteristic of constant current is adopted,and the coil current is only dependent of the primary side.Secondly,the magnetic field should be even,so a coupler structure called single transmitter and double pick-ups is adopted.the mutual inductance between the double pick-ups is introduced as a result of the coupling overlapped D-D coils in the secondary side,which compensates the zero points of mutual inductance between each pick-up coil and the transmitter coil.Some constant mutual inductances have been found from the simulation and experimental results.In addition,the voltage and current stress of the switches is reduced through the parallel output system.Theory analysis and result shows that,the output power is the maximum and the efficiency is closed to the optimal,when each ac equivalent resistance is controlled as the mutul inductive impendance between the pick-ups.At the same time,the current and power are both equally distributed among the pick-ups,the power and efficiency are constant during the entire moving.The PI controllers are realized independently in the each Boost circuit,and the adjust range of duty cycle increases with the load.Finally,a 600 W experimental prototype is set up to validate the proposed system of average current and constant power and efficiency,the result shows that the both output power and efficiency fluctuation are within ±2%.